1. Field of the Invention
This invention relates in general to railroad cars and more specifically, to a one piece center sill and its method of manufacture.
2. Summary of the Prior Art
The center sill is the primary structural member of the underframe of a rail car. It is subjected to the buff and draft forces created during operation of the rail car and normally extends as a continuous member along the length of the car body. In the past, center sills have possessed many different cross-sectional configurations depending on the type of rail car and other considerations. Center sills have been in the shape of hat designs, C-sections and other configurations. Regardless of its particular shape, it is well known to form a center sill by welding a plurality of pieces together as a unit along its substantial length. The use of welds to manufacture center sills presents several long existing problems. Because welding is needed, the reliance on this process to fabricate a finished center sill is inefficient from both a cost and productivity standpoint. The application of the welds along the lengths of the pieces being joined as a center sill is labor intensive and cannot attain high-speed production. In addition, the application of multiple welds heats the material being joined and results in so-called weld flux. Weld flux creates deviations in the straightness or acceptable tolerances of the center sill being formed. As a result, further physical steps are needed to finish the welded center sill unit and conform it to acceptable tolerances in camber, sweep and twist to be suitable for use in a railroad car. As an additional important consideration, a welded center sill is an inherently heavy structure due to its design and fabrication technique. Accordingly, it is desirable in the prior art to provide an improved, light weight center sill in which the necessity of welds or other securement techniques are eliminated.
It is an objective of this invention to provide an improved single piece center sill capable of being cold formed into a straight member having close tolerances. The various configurations of the several embodiments of the invention are cold formed at a plurality of cold rolling stations from a plate or sheet of coiled steel. The flat sheet undergoes progressive formation at each rolling station whereby drawings of the steps of shaping developed by each roll station, when superimposed, form a flower diagram to assist the roll tooling designer. The center sills herein disclosed can be formed on a continuous basis without interruption between separate center sills. The unique cold forming process of the invention allows center sills having a thickness up to one-half inch to be formed without the use of welds as in the prior art. Because the bent sections forming the shape of the center sill are cold worked numerous times during working, the material is strengthened to produce a stronger cross-section without thicker sections or reinforcing material. The center sills are open at the bottom to provide desired access within the center sill body. Two of the configurations of the center sill include extra structural features that provide enhanced strength characteristics without adding significant weight.